Definately take the stroller. Chances are your little guy will need a break at some point.
We take our kids to the fair every year. Here are a few things we do that really make the trip the best it can be.
-Set a budget and get the cash out before you go. That way you won't break the bank, easy to do!
-take drinks with you, no need to pay for water.
-If you plan to eat there take snacks so you won't have to spend money on them.
-Everyone wear the same color.
-First thing, take your son to the police headquarters. They usually register your kids and it's a great time to indroduce your son to a police officer and explain to him that if anything were to happen he would want to find someone dressed like "this" to help him.
I would also go to babies r us and buy a wrist cord. Not sure what they are actually called but they are velcro bands that go around each of your wrists. They have an expandable cord that comes out of each that attatch to eachother with an s hook. That way if your son walks he will always be close. And they are "cooler" for bigger kids than the teddy bear back pack.
Have LOTS of fun.